1. Field of the Invention
This invention relates generally to the field of ion implanted semiconductor materials and more particularly to techniques for producing MESFET devices.
2. Description of the Prior Art
Ion implantation technology has been used for GaAs FET channel formation over the past several years. However, devices made using ion implanted channels have demonstrated inconsistent RF and DC performance. This is because the quality of the channel layer strongly depends on the properties of the semi-insulating substrate, which contains high levels of impurities such as chromium. It is also known that redistribution of impurities takes place when the substrate is heat treated to anneal out the implantation damage.
In spite of inconsistent results associated with the use of ion implantation for the formation of the active channel, this technique provides a number of advantages. These include the possibility of planar type device and circuit technology, good uniformity of the channel layers and economy. For the microwave discrete devices, monolithic integrated circuits and digital integrated circuits, ion implantation continues to offer significant advantages over other technologies. Recently, quarter-micron gate length FET devices have been reported with a noise figure of 1.9 dB and 7 dB associated gain at 18 GHz. Other reports indicate that a noise figure of 1.3 dB with an associated gain of 10 to 11 dB at 12 GHz have been achieved. In all cases, these devices have been fabricated with deeply recessed gate structures (0.3 .mu.m) on 0.5 .mu.m thick active channel layers over high quality buffer layers grown by AsCl.sub.3 /liquid Ga/H.sub.2 vapor phase epitaxy (VPE).
As an advancement in the art, the present invention provides extremely low-noise and low-cost GaAs MESFETs fabricated by new ion implantation techniques without deeply recessed gate structures. The best performance (to date) includes a 1.3 dB noise figure with 10.3 dB associated gain at 12 GHz and a noise figure of 2.3 dB with an associated gain of 7.4 dB at 18 GHz.